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Full text of "The manufacture and properties of iron and steel"

METALLURGY OP IRON AND STEEL.-
and colder, producing no gas and letting steam and air pass through unconsumed. There is a mean between these extremes which is almost forced upon the operator, wherein the fire is kept at a constant temperature, and in this condition there is not much increase in hydrogen from the steam, while a little steam passes away with the gases.
In the upper zone of the fire, the volatile hydrocarbons of the fuel are distilled by the heat beneath, and in this way the gaseous products contain a certain proportion of tarry vapors, part of which is condensed in the conducting tubes. The zones of combustion and distillation are not separated by any arbitrary line, but some of the rich components of the coal are carried down into the body of the fire and exposed to a high temperature. This causes the separation of carbon, some of which is burned with the coal, while the rest is carried forward into the conducting tube. When the fire is hot, large volumes of soot are formed in this way and give trouble in the pipes, but when cool there is little soot, but much tar. The worst condition is when holes form, in the bed of coal. This allows air to come through and burn the hydrocarbons above the fire with a smoky soot-producing flame, cakes the coal into an unworkable mass, and increases the percentage of carbonic acid in the gas.
In Sec. VHIi were discussed certain producer experiments, and the gas "there given may be taken as representative of ordinary practice, the composition being as follows:
Per cent. Siemens   Gas.                                                            by volume.
C02.....................................        5.7
C2H4   ....................................        0.6
O.......................................        0.4
CO......................................      22.0
H  .......................................      10.5
CH4.....................................        2.6
N, by difference...........................     58.2
100.0
Some of these percentages, notably of C02, H, and CH4, vary through wide ranges according to the condition of the fire, but the nitrogen will always be about 60 per cent. This component remains passive throughout all the future history of combustion, but it so reduces the calorific intensity that the gas is applicable only to regenerative furnaces.
The ordinary methods of gas analysis fail to take definite account